Improvements in or relating to electron discharge devices

ABSTRACT

An electron discharge device has a hermetic pinch seal formed by an indium type pressure seal. A method and apparatus for the manufacture thereof are also described. The apparatus comprises a demountable vacuum system having a removable top with ports therein, in one of which is mounted the envelope of the device being manufactured and in the others of which are mounted other envelopes. A rotatable and reciprocable platform in the vacuum chamber carries an evaporator for forming a photoelectric layer in the envelope and an electron gun on a pinch for sealing into the envelope. The platform also carries a test electron gun the beam from which is scanned over the photoelectric layer to test it, and an oven for baking the lower part of the envelope of the device. The various devices mounted on the platform are raised so that they enter respective envelopes for the purpose of degassing them.

[ Oct. 23, 1973 United States Patent [1 1 Sivyer IMPROVEMENTS IN ORRELATING TO ELECTRON DISCHARGE DEVICES [75] Inventor:

Primary Examiner-Charles W. Lanham Assistant ExaminerJ. W, DavieAttorney-Fleit, Gipple & Jacobson Raymond Frank Sivyer,Sunbury-on-Thames, England [73] Assignee: EMI Limited,

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[21] AppL 140 189 method and apparatus for the manufacture thereof arealso described. The apparatus comprises a demountable vacuum systemhaving a removable top with ports Foreign Application Priority Datatherein, in one of which is mounted the envelope of the device beingmanufactured and in the others of May 7, 1970 GreatBritain..,................ 22,195/70 which are mounted other envelopes.A rotatable and reciprocable platform in the vacuum chamber carries anevaporator for forming a photoelectric layer in the envelope and anelectron gun on a pinch for sealing into the envelope. The platform alsocarries a test electron gun the beam from which is scanned over the 0 92 HH... 4 1 N 3 3 [52] US. [51] Int. [58] Field ofSearch;....................

29/25.15, 25.16, DIG. 22; 316/19, l7, l8,

photoelectric layer to test it, and an oven for baking the lower part ofthe envelope of the device. The vari- References Cited UNITED STATESPATENTS 11/1967 ous devices mounted on the platform are raised so thatthey enter respective envelopes for the purpose of degassing them.

3,353,890 Legoux. 2,984,759 5/1961 Vine 4 Claims, 3 aw T315255.

Patentd 0a. 23, 1973 3,767,283

2 Sheets-Sheet 1 a Iiihrm y IMPROVEMENTS IN OR RELATING TO ELECTRONDISCHARGE DEVICES This invention relatesto electron discharge devices,such as television pick-up tubes, and to methods of and apparatus formaking them.

It is common practice to provide at the base of a photoelectric device apinch seal formed by heat fusing to the glass envelope a glass basehaving wires hermetically sealed therethrough for making electricalconnectionsto the various electrodes.

This form of pinch seal suffers from several disadvantages, among'whichare the need for a relatively high temperature to effect the fusion ofthe base to the envelope which may result in the release of a gas orgases having a deleterious effect 'on the photoelectric surface; arelatively lengthy processing time is required owing to the need for asecond pumping schedule to remove the gases released during the mainsealing process; the accuracy of the positioning of the electrodestructure may be adversely affected due to movement when the glassbecomes softened to make the seal; and, especially with hard glassenvelopes and bases, the choice of suitable materials for the sealedthrough wires of the base becomes rather limited and is conventionallytungsten. Tungsten isdifficult to seal to glass and wires of the sizeemployed for these devices are brittle and are easily broken.

It is an object of the invention to provide an improved method of anelectron discharge device making.

According to the invention there is provided a method of making anelectron discharge device including the following steps:

a. providing a vitreous envelope closed by a window at one end andhaving a smooth edge surface at its other end,

b. providing for said envelope a closure member having electricallyconductive wires hermetically sealed therethrough and an electron gunstructure connected to said wires, said closure member having a smoothsurface portion for co-operating with said smooth edge surface of saidenvelope,

0. mounting said closure member with said electron gun in an evacuablechamber,

d. mounting said envelope in a port in said chamber so as tohermetically seal said port with said open end of said envelope incommunication with said chamber, the window end of said envelopeprotruding from said chamber, and evacuating said chamber and saidenvelope,

e. testing said device, and I f. subsequently hermetically sealingtogether under vacuum said smooth edge surface of said envelope and saidco-operating smooth surface portion of said closure member by means ofan indium type pressure seal.

By the term indium type pressure seal used herein is meant any hermeticseal formed by compressing between surfaces to be joined a soft metalsuch as indium or indium alloyed with other metal, for example anindiumtin alloy, or other materials having sealing properties similar toindium.

In order that the invention may be clearly understood and readilycarried into effect it will now be described by way of example withreference to the accompanying drawings in which:

' FIG; 1 illustrates diagrammatically one example of an electrondischarge device made by a method according to the invention,

FIG. 2 illustrates diagrammatically a perspective view of apparatus formaking a photoelectric device, and

FIG. 3 illustrates diagrammatically a sectional view of part of theapparatus of FIG. 2 in which an electron discharge device is ready forfinal sealing.

Referring to the drawing, FIG. 1 shows one example of an electrondischarge device in the form of a television pick-up tube. The pick-uptube comprises a vitreous envelope 1 to which are hermetically sealed awindow 2 and a vitreous closure member (or pinch seal) 3 having pinssuch as 4 hermetically sealed therethrough. An electron gun indicatedgenerally by the reference numeral 5 is mounted on the pins 4 andcentred in the envelope I by means of spacers 6 and 7. On the innersurface of the window 2 is a substantially transparent layer 8 of anelectrically conducting material, such as a Nesa coating, which extendsfor a small distance along the surface of the envelope 1. On the layer 8is a layer 9 of a photoelectrically sensitive material, lead oxide forexample. A platinum wire or strip 10 is hermetically sealed through theenvelope 1 to provide electrical connection to the Nesa coating from anexternal contact ring 11. The vitreous closure member 3 is hermeticallysealed to the envelope 1 by means of an indium ring 12 surrounded by astainless steel ring 13. If desired, the pinch seal may be overcapped inknown manner. The envelope 1 is made from precision bore tubing of avitreousmaterial such as Pyrex and the end to which the pinch seal is tobe made is cut to the correct length and ground and polished to providea smooth reference surface which assists in making the seal. The closuremember 3 has two annular ground and polished regions 3a and 3b (as shownmore clearly in FIG. 3) to assist in making the seal, the region 3a alsoacting as a reference surface co-operating with the polished edge oftheenvelope to aid in the positioning of the electron gun structure 5 ofthe device.

Reference is now made to FIGS. 2 and 3 which show apparatus for themanufacture of an electron discharge device. The apparatus comprises ademountable vacuum pump system having a vacuum chamber 20 and a top 21releasably secured thereto in airtight relationship by means such asbolts (not shown). A rotatable platform 22 is supported below top 21 bymeans of a support rod 23 secured to platform 22 and passing through ashaft seal 24 in which vacuum is applied to the space between twosealing rings. The support rod 23 has a handle 23a whereby the platform22 can be raised and lowered relative to the top 21. Two guide rods 25are secured to the underside of the top 21 and platform 22 is providedwith four indexing apertures 26, spaced at around the axis of supportrod 23, through which the guide rods can slide so that the platform 22can only be raised in one of four positions.

Spaced at 90 around the axis are four apertures or ports in the top 21,in one of which, 27, the envelope 1 is mounted in an airtight manner.The other three apertures have envelopes 28, 29 and 30 mounted thereinin an airtight manner. The envelope I is mounted on the top 21 by meansof a vacuum sealing ring 31 and plate 32, a further sealing ring 33 andclamping plate 34 being provided to prevent the envelope 1 from beingsucked through aperture 27 when the chamber 20 is evacuated. Theenvelopes 1, 28, 29 and 30 are all mounted on the top 21 at the sameradius from the axis of the support rod 23, which is the axis ofrotation of the platform 22. Mounted on the platform 22 at this sameradius and spaced at 90 around the axis are four stations containingrespectively, the electron gun 5 mounted on the closure member 3, anoven 35 for outgassing the lower part of envelope 1, an electron gun 36plugged into a socket 36a for testing purposes, and an evaporator 37surrounded by a glass tube 38. Electrical connections are made to eachof these four stations from a respective socket 39, the connectionsbeing made below platform 22 and indicated by the dashed lines 40. Thesockets 39 are mounted at 90 around the axis of rotation at a commonradius. Two plugs 41 are mounted on the top 21. spaced at 90 apart onthe same radius as the sockets 39 such that when the platform 22 israised two of the sockets 39 engage with the plugs 41. The plugs 41provide airtight sealed through electrical connections for the units forthe time being in the envelope 1 and 30.

There will now be described by way of example the manufacture of anelectron discharge device. With the top 21 removed from the chamber 20and' with the platform 22 in its lowered position, an envelope 1provided with a window 2, Nesa coating 8 and sealed through connection10 is mounted in the top 21 so that the lower part of the envelopeprotrudes below the top 21'; the evaporator is charged with material toprovide the photoelectrically sensitive layer 9; the electron gun 5mounted on closure member 3 is plugged into a socket (not shown) in asupport block 42 mounted on the platform 22, with the interpositionbetween closure member 3 and support block 42 of a washer 43 of amaterial such as a soft metal, lead for example, so as to reduce thechances of the closure member 3 cracking or chipping when sealingpressure is subsequently applied; the test electron gun 36 is pluggedinto the socket 36a, the life of the electron gun 36 being such that itcan be used in the manufacture of several electron discharge devices;and a freshly turned indium fillet 12 in a stainless steel ring 13 isprovided and may be slid over the electron gun 5 to rest against closuremember 3 (as shown in FIG. 3), but which is preferably located away fromthe closure member by clips (not shown) below envelope 29 so that theelectron gun 5 and the closure member 3 may be outgassed at a highertemperature. The top 21 is then secured in airtight manner to the vacuumchamber 20 which is evacuated by a vacuum pump 44 connnected to chamber20 at 45.

With the platform 22 positioned relative to the top 21 as shown in FIG.2, platform 22 is raised. In so doing, the oven 35 fits around the lowerend of the envelope 1; the electron gun 5 enters envelope 30; theelectron gun 36 enters envelope 28; and the evaporator 37 and tubularsurround 38 enter envelope 29, passing through the indium fillet 12supported therebelow. The oven 35 and the electron gun 5 are connectedthrough their respective sockets 39 and plugs 41 to an external powersupply (not shown). Eddy current heating coils are placed around theenvelopes 28, 29 and 30 to outgas the electron guns and'the evaporator,the lower end of envelope 1 is baked by the oven 35 and the cathode ofelectron gun 5 is activated. The envelope 1 is raised to the positionshown in FIG. 3. Oxygen from a supply 46 may be introduced at 47 orother neutral gas such as nitrogen from an auxiliary gas supply 48 maybe introduced at 49 to assist in raising the envelope 1, after which thevacuum chamber 20 is again evacuated. The upper part of envelope 1 isoutgassed by means of an oven placed therearound and may be maintainedin a heated condition until after the photosensitive layer has beenevaporated. Next, electron gun 36 is transferred from envelope 28 toenvelope 1 by lowering platform 22, rotating it through and raising itagain. The electron gun 36 is arranged to occupy the position which theelectron gun 5 will occupy after sealing. The electron gun 36 is thenoperated and the Nesa coating 8 is tested by scanning the electron beamthereacross, with the aid of focus and deflection coils placed aroundthe envelope 1, signals being taken from the sealed through connection10. This test will show up blemishes which may not show up under opticaltesting. If the'Nesa coating is unsatisfactory, the manufacturingprocess may be halted at this stage and the faulty envelope I replacedby a fresh one. If the Nesa coating is satisfactory, the manufacturingprocess passes to the next stage.

At the same time as the electron gun 36 is being raised into theenvelope 1, the electron gun 5 is being raised into the envelope 29below which is located by clips the indium fillet 12 in the stainlesssteel ring 13. The electron gun 5 passes through the indium fillet andthe clips are then released so that the indium is supported around theedge of the closure member 3.

At this stage, the evaporator 37 is within the envelope 28 and it is nowtransferred to the envelope 1 by again lowering, rotating and raisingthe platform 22. A heat sink, for example a vessel containing glycerineat a suitable temperature, is placed on the window 2. Photoelectricallysensitive material is evaporated from the evaporator 37 and condensesonto the Nesa coating 8 to form the photoelectric layer 9 on the window2. When the evaporation process is finished, the oven and heat sink areremoved from the envelope 1 and the electron gun 36 is re-insertedtherein. The focus and deflection coils are again placed around theenvelope 1 and an optical image is projected onto the window 2. Thephotoelectric layer 9 is tested by operating the electron gun 36 andcausing the electron beam to be scanned across the layer9. The signalsthus produced are taken out via the sealed through connection 10, whichsignals are then used to test the layer 9 in respect of, for example,resolution, the presence of target blemishes, sensitivity and lag. Ifthe tests show the photoelectric layer 9 to be satisfactory, it may thenbe further processed. For example, the layer 9 may be subjected to acorona discharge, employing the mesh of the electron gun 36 as thecorona discharge electrode, to stabilise the layer 9. The coronadischarge may be carried out in an oxygen atmosphere in the case of alead oxide photoelectric layer. The layer 9 may also be subjected togaseous treatments, and, if desired, further evaporated layers may bedeposited.

The layer 9 may be retested by again causing an electron beam from theelectron gun 36 to scan thereacross. If a satisfactory result is againobtained, the envelope is ready for sealing. This is achieved byinserting the electron gun 5 into the envelope 1, as shown in FIG. 3.From the position shown in FIG. 3, the platform 22 is raised so that thestainless steel ring 13 enters the aperture 27 in the table top 21 inwhich it is a sliding fit. A pair of rotatable members 50 having flanges51 are rotated to move the flanges into recesses 52 in the support block42. Sealing rings 53 are positioned between the rotatable members 50 andthe top 21 to maintain the vacuum in the chamber 20. With the supportblock 42 supported on the flanges 51, clamping plate 34 is retion mayhave a second evaporator containing other material to be evaporated ontothe photoelectric layer.

What we claim is: l. A method of making an electron discharge deviceleased and pressure applied, for example by means of 5 i l ding thefollowing steps:

an air cylinder, to push the lower end of envelope 1 against the indiumfillet 12 to provide an hermetic seal.

After removal from the pump table, the electron discharge device isprovided with the contact ring 11, overcapping of the pinch seal ifdesired, and focus and deflection coils.

it will thus be seen that an electron discharge device made by a methodaccording to the invention has several advantages over previous devicesand methods. One advantage is that due to the indium type pressure seal,no gases are envolved during sealing which might deleteriously affectthe photoelectric layer and which would require a further pumpingoperation, thus providing a considerable saving of time and materials.Also, because the Nesa and photoelectric layers are tested underintended running conditions without sealing the device, if either layershould prove faulty then manufacture can be terminated at that point oradditional processing may be carried out to correct the faults, thusproviding a further savingof time and materials compared with methods inwhich testing is done only after final sealing has occurred. Anotheradvantage of the method of testing the photoelectric layer as describedherein is that as the test electron gun occupies the position to beoccupied by the final electron, gun, the signals obtained by thetestelectron gun are identical with those obtainable in the completeddevice. Yet a further advantage obtained by the preferred methoddescribed herein is that as the indium ring is supported away from theclosure member and its electron gun during degassing thereof, thedegassing of the gun and closure member can be carried out at a highertemperture. A further advantage still is that the overall length of anelectron discharge device can be reduced, one of the reasons being thatthe electron gun can be degassed closer to the closure member if theindium ring is supported elsewhere.

It will be appreciated that, if desired, the test electron gun 36 may beomitted and the electron gun 5 employed also as the test gun. in thiscase, pick up of the indium ring by the electron gun 5 and closuremember 3 may be delayed until after the tests have been carried out.With this arrangement, only three ports or apertures in the top 21 andthree stations on platforms 22 are required.

Also, if desired, more than four stations with corresponding ports maybe employed. For example, a fifth station may have a corona dischargeelectrode, instead of employing the mesh of the electron gun. A sixthstaa. providing a vitreous envelope closed by a window at one end andhaving a smooth edge surface at its open end,

b. providing for said envelope a closure member having electricallyconductive wires hermetically sealed therethrough and an electron gunstructure connected to said wires, said closure member having a smoothsurface portion for co-operating with said smooth edge surface of saidenvelope,

c. supporting said closure member with said electron gun in an evacuablechamber,

d. mounting said envelope in a port in said chamber so as tohermetically seal said port with'said open end of said envelope incommunication with said chamber, the window end of said envelopeprotruding from said chamber, and evacuating said chamber and saidenvelope,

e. testing said device, and

f. subsequently hermetically sealing together under vacuum said smoothedge surface of said envelope and said co-operating smooth surfaceportion of said closure member by means of an indium type pressure seal.

2. A method according to claim 1 including the steps of providing insaid evacuable chamber an evaporator containing material for producing aphotosensitive target layer, producing a photosensitive target layer onsaid window of said envelope, and subsequently testing said devicebefore making said hermetic pressure seal.

3. A method according to claim 1 including the steps of supporting onsaid closure member a ring of material for effecting said hermeticpressure seal, supporting said closure member below said envelope andapplying pressure to said envelope to cause it, without breaking thevacuum seal, to contact said ring and effect said hermetic pressure sealbetween said envelope and said closure member. 7

4. A method according to claim 2 including the step, prior to producingsaid target layer, of baking said envelope while mounted in said port,the lower part of said envelope being baked in the evacuated chamber andthe upper part of said envelope being baked outside said chamber, andincluding the step of baking said closure member and electron gun at aposition remote from target material, said baking being effected at atemperature higher than that which is attained in the normal operationof said device.

1. A method of making an electron discharge device including thefollowing steps: a. providing a vitreous envelope closed by a window atone end and having a smooth edge surface at its open end, b. providingfor said envelope a closure member having electrically conductive wireshermetically sealed therethrough and an electron gun structure connectedto said wires, said closure member having a smooth surface portion forco-operating with said smooth edge surface of said envelope, c.supporting said closure member with said electron gun in an evacuablechamber, d. mounting said envelope in a port in said chamber so as tohermetically seal said port with said open end of said envelope incommunication with said chamber, the window end of said envelopeprotruding from said chamber, and evacuating said chamber and saidenvelope, e. testing said device, and f. subsequently hermeticallysealing together under vacuum said smooth edge surface of said envelopeand said co-operating smooth surface portion of said closure member bymeans of an indium type pressure seal.
 2. A method according to claim 1including the steps of providing in said evacuable chamber an evaporatorcontaining material for producing a photosensitive target layer,producing a photosensitive target layer on said window of said envelope,and subsequently testing said device before making said hermeticpressure seal.
 3. A method according to claim 1 including the steps ofsupporting on said closure member a ring of material for effecting saidhermetic pressure seal, supporting said closure member below saidenvelope and applying pressure to said envelope to cause it, withoutbreaking the vacuum seal, to contact said ring and effect said hermeticpressure seal between said envelope and said closure member.
 4. A methodaccording to claim 2 including the step, prior to produciNg said targetlayer, of baking said envelope while mounted in said port, the lowerpart of said envelope being baked in the evacuated chamber and the upperpart of said envelope being baked outside said chamber, and includingthe step of baking said closure member and electron gun at a positionremote from target material, said baking being effected at a temperaturehigher than that which is attained in the normal operation of saiddevice.